1. Field of the Invention
The disclosed methods and apparatus relate broadly to electronic integrated circuits (“ICs”), and more specifically to interfacing IC dies to circuits in which they are employed.
2. Related Art
ICs must generally be connected to external circuitry to be useful, and the interconnection itself may impact the net high frequency performance of the IC. For example, FIG. 1 illustrates an exemplary SPDT analog switching circuit. A first high frequency signal, RF1, is input to pin 3. A second high frequency signal, RF2, is input to pin 13. Control signals provided between pins 16 or 17 and 19 (GND) determine whether an RF common connection RFC is coupled to RF1 or to RF2. This particular exemplary analog switch provides switchable resistive termination into 75 ohms for any one of the three signal connections (RF1, RF2 or RFC) that is not otherwise properly terminated for RF signals.
An IC as shown in FIG. 1 may be employed in electronic devices that have stringent isolation requirements. Such requirements may derive from functional performance needs of the equipment employing the IC. Often, however, isolation requirements between terminals are defined by regulations that have little or nothing to do with adequate performance. Circuits such as the switch illustrated in FIG. 1 may be subject, for example, to the isolation requirements of FCC Part 15.115. These requirements include, among others, a requirement for isolation of −80 dB between any two of the signal lines RF1 and RF2 at a range of frequencies up to 216 MHz. Other regulations, and/or performance requirements, may establish correspondingly different isolation requirements.
An integrated circuit (IC) alone might satisfy such isolation requirements, yet fail when packaged in a carrier. A carrier typically provides a mounting and protection for an IC, together with terminals that are more readily connected to an external circuit than would be the connections, or pads, on the IC itself. Techniques by which the IC is protected and connected to the carrier may impair the inherent signal isolation provided by the IC alone. The interconnection techniques described herein help to satisfy both performance needs and regulatory requirements by minimizing the degradation of IC signal isolation that may be caused by mounting in a carrier.